The present invention relates to a lubrication device of a turbocharger of an engine for a vehicle, and in particular relates to the one in which a first turbocharger and a second turbocharger are provided at a one-side wall of the engine, the second turbocharger being located above the level of the first turbocharger.
Conventionally, a turbo charging device to supercharge intake air by using the kinetic energy of exhaust gas exhausted from an engine is known. Further, a sequential type of turbo charging device, in which there are provided a small-sized turbocharger to supercharge the intake air mainly at a low engine-speed and low load and a large-sized turbocharger to supercharge the intake air mainly at a high engine-speed and high engine-load, and supercharging characteristics of the turbochargers are selectable in accordance with an engine's operation state, is known.
In the turbo charging device disclosed in U.S. Pat. No. 6,782,849, the large-volume first turbocharger and the small-volume second turbocharger are provided at the one-side wall of the engine, the second turbocharger being located above the level of the first turbocharger, the compressor of the second turbocharger being arranged downstream of the compressor of the first turbocharger, and the intercooler is arranged upstream of the coolant's cooler and between the compressor of the first turbocharger and the compressor of the second turbocharger. According to this device, the length of the intake-air pipe between the intercooler and the compressor of the second turbocharger can be shorter, so that the layout space can be improved.
In the turbo charging device disclosed in Japanese Patent Laid-Open Publication No. 2006-70878, the small-sized turbocharger, the large-sized turbocharger, the DPF (Diesel Particulate Filter) connected to the turbine outlet of the large-sized turbocharger are provided at the one-side wall of the engine, the large-sized turbocharger being arranged below the small-sized turbocharger, the DPF being located below the small-sized turbocharger and substantially at the level of the large-sized turbocharger so that the exhaust-gas induction port thereof opens on the side of the turbine of the large-sized turbocharger. According to this device, the DPF and turbochargers can be provided compactly on the one-side wall of the engine, and the exhaust gas with less exhaust-energy loss and higher temperature can be obtained.
The turbine shaft of the turbo charging device is rotatably supported at the oil-lubrication type of the shaft bearing portion in the center housing. Herein, the turbine driven by the exhaust-gas kinetic energy rotates at a high engine-speed exceeding 200,000 rpm, so it is essential to improve the function of the lubrication device which lubricates the shaft bearing portion in order to secure the reliability of the turbo charging device.
In the turbo charging device disclosed in Japanese Patent Laid-Open Publication No. 2007-309124, there are provided the turbocharger, the center housing as the shaft bearing portion to support the turbine shaft, the oil supply passage to connect the cylinder block and the center housing, the metal-made oil return passage to connect the lower face of the center housing and the lower end portion of the cylinder block, the exhaust manifold and three-way catalyst and the like which are arranged in the upper-and-rear side space. The heat-insulating plate is attached to the oil return passage so as to divide the space into the upper-and-rear side space and the lower-and-front side space. According to this device, the heat influence of the heat-insulating plate for the lower-and-front side space is prevented, so that any heat-sensitive member, such as rubber pipe or a synthetic-resin made component, can be attached. Herein, this patent publication discloses, in the column of background art, the rubber-made oil return passage which is covered with the heat insulating plate at part of its surface to improve against the vibration move of the turbocharger relative to engine.
According to the turbo charging device disclosed in the above-described third patent publication, since the oil return passage is made from metal, it may be possible to arrange the heat-sensitive components without causing any heat damage to the oil return passage disposed in the vicinity of a heat source, such as the exhaust manifold or the three-way catalyst. However, in the case of the two turbochargers being provided at the side wall of the engine as disclosed in the above-described first and second patent publications, the following problems may occur newly.
First, since the two turbochargers are provided at the side wall of the engine, each of the turbochargers requires the housing, oil passage for supply and return, cooling water passage for supply and return, and others, in addition to the passage for exhaust gas connecting the turbochargers, so that the layout of components around the engine may become difficult. Therefore, there is a concern that arrangement of components, such as engine supplemental parts or engine-side connection portions of the oil return passages and the like, may become difficult.
Secondly, each turbocharger has its assembly error and vibration move relative to the engine's side wall. Therefore, when the intake and exhaust passages of the turbo chargers are connected, the assembly error of one of the turbochargers relative to the engine-side connection portion may influence the assembly error of the oil return passage of the other turbocharger relative to the engine-side connection portion. Accordingly, there is a concern that the assembly error of the two turbochargers may increase compared to the case of assembling a single turbocharger. Further, in the case of the two turbochargers being assembled, the layout space becomes narrower and the heat-source number increases, so that the rubber-made oil return passage may also have its heat damage as well.